Real-Time Hybrid Simulation and Power Hardware-in-the-Loop characterization of distribution grid models

Kurzfassung

The grid codes implemented by several countries demands distributed generators to provide voltage support through provision of reactive power by inverters. With increasing inverter-based generation it is essential to test local autonomous control of inverters in a controlled environment to investigate grid stability. Real-time power hardware-in-the-loop (PHIL) concept is an efficient tool for such evaluations. This thesis focuses on the development of a PHIL setup to examine the issues linked with the power interface and also the hardware under test when it is controlled virtually to inject/draw desired powers into/from the simulated grid. In the first phase, a simulation testbed is developed which includes distribution grid models following the topology from MONA projects. The models are developed completely in the phasor domain which enables to perform dynamic power flow and voltage stability analysis. The feed-in unit and the load are integrated with actual power profiles. It is a hybrid load modelled as a grid following inverter injecting synchronized currents into the grid based on power sink or feed-in. For reactive power management during the feed-in, smart inverter control functions are developed. Different reactive power control strategies are tested and its impact on the grid voltage is observed. For validation of the grid model and reactive power management functions, the results of some scenarios are compared from two different power distribution system analysis platforms. In the second phase, a hybrid simulation (Phasor – EMT) model is developed. The aim is to have an interface to facilitate the handling of discrete waveforms during PHIL simulation. The equivalent circuits (Norton and Thevenin) are used to represent one sub-system in another and to ensure proper transfer of variables over the interface bus where the network partition is performed. The scenarios implemented to observe the operation of the developed hybrid simulation model show that the parameters (voltage and current) at the interface bus from both the domains are transformed accurately. Further, the uni-directional and bi-directional power exchange is also analyzed at the interface bus. Finally, in the last phase, the PHIL simulation is executed with MONA-8002 distribution grid simulated in real-time. Proposed unconventional PHIL setup involves two physical hardware components; a power interface (voltage-controlled amplifier) serving as grid-simulator and other as hardware under test (current-controlled amplifier) controlled from the simulation platform. The mathematical model is executed on multi-core processors of real-time simulator with a sample time of 100 µs. Going lower than this causes the processors to overload. Different configurations of hardware under test at the point of common coupling are tested with the virtual simulated grid. The results show that the hardware in amplifier mode injects reactive power into the virtual grid depending upon the voltage level due to its parasitic capacitance. At nominal standard voltage, a capacitive reactive power of roughly 1.3 kvar is present. Further at low power demands, the current waveform gets very distorted due to the increased harmonic content. To alleviate the effects of parasitic capacitance two compensation methods are introduced and tested. After implementing the compensation, the average default reactive power from the hardware under test i.e. current-controlled amplifier is reduced.